Transmission, Distribution & Storage

Soil corrosion and hydrogen embrittlement are the main factors of hydrogen pipeline failure. The gas escapes diffuses and accumulating in the soil and entering the atmosphere when leak occurs. The mechanism of gas diffusion in buried pipelines is very complicated. Mastering the evolution law of hydrogen leakage diffusion is conducive to quickly locating the leakage point and reducing the loss. The leakage model of the underground hydrogen pipeline is established in this paper. Effect of leakage hole soil type pipeline pressure pipeline diameter on hydrogen leakage diffusion were investigated. The results show that when the hydrogen pipeline leaks the hydrogen concentration increases with the increase of leakage time showing a symmetrical distribution trend. With the pipeline pressure increase hydrogen leakage speed is accelerated and longitudinal diffusion gradually becomes the dominant direction. With the leakage diameter increases hydrogen leakage per unit of time increases sharply. Hydrogen diffuses more easily in sandy soil and diffusion speed concentration and range are higher than that in clay soil. The research content provides a reference and basis for the detection and evaluation of buried hydrogen pipeline leakage.

Energy storage is an effective way to address the instability of renewable energy generation modes such as wind and solar which are projected to play an important role in the sustainable and low-carbon society. Economics and carbon emissions are important indicators that should be thoroughly considered for evaluating the feasibility of energy storage technologies (ESTs). In this study we study two promising routes for large-scale renewable energy storage electrochemical energy storage (EES) and hydrogen energy storage (HES) via technical analysis of the ESTs. The levelized cost of storage (LCOS) carbon emissions and uncertainty assessments for EESs and HESs over the life cycle are conducted with full consideration of the critical links for these routes. In order to reduce the evaluation error we use the Monte Carlo method to derive a large number of data for estimating the economy and carbon emission level of ESTs based on the collected data. The results show that lithium ion (Li-ion) batteries show the lowest LCOS and carbon emissions at 0.314 US$ kWh-1 and 72.76 gCO2e kWh-1 compared with other batteries for EES. Different HES routes meaning different combinations of hydrogen production delivery and refueling methods show substantial differences in economics and the lowest LCOS and carbon emissions at 0.227 US$ kWh-1 and 61.63 gCO2e kWh-1 are achieved using HES routes that involve hydrogen production by alkaline electrolyzer (AE) delivery by hydrogen pipeline and corresponding refueling. The findings of this study suggest that HES and EES have comparable levels of economics and carbon emissions that should be both considered for large-scale renewable energy storage to achieve future decarbonization goals.

Salt caverns produced by solution mining in Southern Ontario provide ideal spaces for gas storage due to their low permeability. Underground hydrogen storage (UHS) is an important part of the future renewable energy market in Ontario in order to achieve global carbon neutrality and to fill the gap left by retiring nuclear power plants. However large-scale hydrogen storage is still restricted by limited storage space on the ground’s surface. In this study hydrogen’s physical and chemical properties are first introduced and characterized by low molecular weight high diffusivity low solubility and low density. Then the geological conditions of the underground reservoirs are analyzed especially salt caverns. Salt caverns with their inert cavity environments and stable physical properties offer the most promising options for future hydrogen storage. The scales heights and thicknesses of the roof and floor salt layers and the internal temperatures and pressures conditions of salt caverns can affect stabilities and storage capacities. Finally several potential problems that may affect the safe storage of hydrogen in salt caverns are discussed. Through the comprehensive analysis of the influencing factors of hydrogen storage in salt caverns this study puts forward the most appropriate development strategy for salt caverns which provides theoretical guidance for UHS in the future and helps to reduce the risk of large-scale storage design.

The on-board hydrogen storage of mobile applications is a key area of global industrial transformation to hydrogen technology. The research work provides an overview about the principle of hydrogen fuel cell vehicles with a focus on the widespread on-board hydrogen storage technologies. In this work type IV composite pressure vessels in particular are reviewed. The key challenges of polymeric liners are deeply investigated and liner collapse was identified as a critical failure of type IV vessels. Different factors of liner collapse were categorized and relevant material properties - such as permeability physical characteristics and surface properties - were explained in more detail to lay the foundation for further research on high barrier durable polymeric liner materials.

Smart energy networks provide an effective means to accommodate high penetrations of variable renewable energy sources like solar and wind which are key for the deep decarbonisation of energy production. However given the variability of the renewables as well as the energy demand it is imperative to develop effective control and energy storage schemes to manage the variable energy generation and achieve desired system economics and environmental goals. In this paper we introduce a hybrid energy storage system composed of battery and hydrogen energy storage to handle the uncertainties related to electricity prices renewable energy production and consumption. We aim to improve renewable energy utilisation and minimise energy costs and carbon emissions while ensuring energy reliability and stability within the network. To achieve this we propose a multi-agent deep deterministic policy gradient approach which is a deep reinforcement learning-based control strategy to optimise the scheduling of the hybrid energy storage system and energy demand in real time. The proposed approach is model-free and does not require explicit knowledge and rigorous mathematical models of the smart energy network environment. Simulation results based on real-world data show that (i) integration and optimised operation of the hybrid energy storage system and energy demand reduce carbon emissions by 78.69% improve cost savings by 23.5% and improve renewable energy utilisation by over 13.2% compared to other baseline models; and (ii) the proposed algorithm outperforms the state-of-the-art self-learning algorithms like the deep-Q network.

Replacement of fossil fuels with clean hydrogen has been recognized as the most feasible approach of implementing CO2-free hydrogen economy globally. However large-scale storage of hydrogen is a critical component of hydrogen economy value chain because hydrogen is the lightest molecule and has moderately low volumetric energy content. To achieve successful storage of buoyant hydrogen at the subsurface and convenient withdrawal during the period of critical energy demand the integrity of the underground storage rock and overlying seal (caprock) must be assured. Presently there is paucity of information on hydrogen wettability of shale and the interfacial properties of H2/brine system. In this research contact angles of shale/H2/brine system and hydrogen/brine interfacial tension (IFT) were measured using Krüss drop shape analyzer (DSA 100) at 50 ◦C and varying pressure (14.7–1000 psi). A modified form of sessile drop approach was used for the contact angles measurement whereas the H2- brine IFT was measured through the pendant drop method. H2-brine IFT values decreased slightly with increasing pressure ranging between 63.68◦ at 14.7 psia and 51.29◦ at 1000 psia. The Eagle-ford shale with moderate total organic carbon (TOC) of 3.83% attained fully hydrogen-wet (contact angle of 99.9◦ ) and intermediate-wet condition (contact angle of 89.7◦ ) at 14.7 psi and 200 psi respectively. Likewise the Wolf-camp shale with low TOC (0.30%) attained weakly water-wet conditions with contact angles of 58.8◦ and 62.9◦ at 14.7 psi and 200 psi respectively. The maximum height of hydrogen that can be securely trapped by the Wolf-camp shale was approximately 325 meters whereas the value was merely 100 meters for the Eagle-ford shale. Results of this study will aid in assessment of hydrogen storage capacity of organic-rich shale (adsorption trapping) as well as evaluation of the sealing potentials of low TOC shale (caprock) during underground hydrogen storage.

The central objective of this study is to improve the understanding of flow behaviour during hydrogen (H2) storage in subsurface porous media with a cushion gas of carbon dioxide (CO2). In this study we investigate the interactions between various factors driving the flow behaviour including the underlying permeability heterogeneity viscous instability and the balance between the viscous and gravity forces. In particular we study the impact of CO2 solubility in water on the level of H2 purity. This effect is demonstrated for the first time in the context of H2 storage. We have performed a range of 2D vertical cross-sectional simulations at the decametre scale with a very fine cell size (0.1 m) to capture the flow behaviour in detail. This is done since it is at this scale that much of the mixing between injected and native fluids occurs in physical porous media. It is found that CO2 solubility may have different (positive and negative) impacts on the H2 recovery performance (i.e. on the purity of the produced H2) depending on the flow regimes in the system. In the viscous dominated regime the less viscous H2 may infiltrate and bypass the cushion gas of CO2 during the period of H2 injection. This leads to a quick and dramatic reduction in the H2 purity when back producing H2 due to the co-production of the previously bypassed CO2. Interestingly the impurity levels in the H2 are much less severe in the case when CO2 solubility in water is considered. This is because the bypassed CO2 will redissolve into the water surrounding the bypassed zones which greatly retards the movement of CO2 towards the producer. In the gravity dominated scenario H2 accumulates at the top of the model and displaces the underlying cushion gas in an almost piston-like fashion. Approximately 58% of H2 can be recovered at a purity level above 98% (combustion requirements by ISO) in this gravity-dominated case. However when CO2 solubility is considered the H2 recovery performance is slightly degraded. This is because the dissolved CO2 is also gradually vaporised during H2 injection which leads to an expansion of mixing zone of CO2 and H2. This in turn reduces the period of high H2 purity level (>98%) during back-production.

Hydrogen as an energy carrier is very versatile in energy storage applications. Developments in novel sustainable technologies towards a CO2-free society are needed and the exploration of all-solid-state batteries (ASSBs) as well as solid-state hydrogen storage applications based on metal hydrides can provide solutions for such technologies. However there are still many technical challenges for both hydrogen storage material and ASSBs related to designing low-cost materials with low-environmental impact. The current materials considered for all-solid-state batteries should have high conductivities for Na+ Mg2+ and Ca2+ while Al3+-based compounds are often marginalised due to the lack of suitable electrode and electrolyte materials. In hydrogen storage materials the sluggish kinetic behaviour of solid-state hydride materials is one of the key constraints that limit their practical uses. Therefore it is necessary to overcome the kinetic issues of hydride materials before discussing and considering them on the system level. This review summarizes the achievements of the Marie Skłodowska-Curie Actions (MSCA) innovative training network (ITN) ECOSTORE the aim of which was the investigation of different aspects of (complex) metal hydride materials. Advances in battery and hydrogen storage materials for the efficient and compact storage of renewable energy production are discussed.

This work discusses the design and demonstration of an in-situ test setup for testing pipeline steels in a high pressure gaseous hydrogen (H2 ) environment. A miniature hollow pipe-like tensile specimen was designed that acts as the gas containment volume during the test. Specific areas of the specimen can be forced to fracture by selective notching as performed on the weldment. The volume of H2 used was minimised so the test can be performed safely without the need of specialised equipment. The setup is shown to be capable of characterising Hydrogen Embrittlement (HE) in steels through testing an X60 pipeline steel and its weldment. The percentage elongation (%El) of the base metal was found to be reduced by 40% when tested in 100 barg H2 . Reduction of cross-sectional area (%RA) was found to decrease by 28% and 11% in the base metal and weld metal respectively when tested in 100 barg H2 . Benchmark test were performed at 100 barg N2 pressure. SEM fractography further indicated a shift from normal ductile fracture mechanisms to a brittle transgranular (TG) quasi-cleavage (QC) type fracture that is characteristic of HE.

This paper presents a case study of using hydrogen for large-scale long-term storage application to support the current electricity generation mix of South Australia state in Australia which primarily includes gas wind and solar. For this purpose two cases of battery energy storage and hybrid battery-hydrogen storage systems to support solar and wind energy inputs were compared from a techno-economical point of view. Hybrid battery-hydrogen storage system was found to be more cost competitive with unit cost of electricity at $0.626/kWh (US dollar) compared to battery-only energy storage systems with a $2.68/kWh unit cost of electricity. This research also found that the excess stored hydrogen can be further utilised to generate extra electricity. Further utilisation of generated electricity can be incorporated to meet the load demand by either decreasing the base load supply from gas in the present scenario or exporting it to neighbouring states to enhance economic viability of the system. The use of excess stored hydrogen to generate extra electricity further reduced the cost to $0.494/kWh.